current on a grounding electrode conductor

Status
Not open for further replies.

ryagesh

Member
Could you please let me know what is acceptable current on the grounded electrode conductor for a new 120/240V Single phase system.
Thanks B.Y.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: current on a grounding electrode conductor

That is a hard question to answer. Typically less than 1-amp. If you have an extremely low ground electrode system (GES) impedance, and a lot of unbalanced load current on the neutral (grounded circuit conductor) it can approach 1-amp. There will always be some current, if not you have probably got a different problem like a poor connection in the GEC, MBJ, or extremely poor GES.

On the other hand if there is a problem with the neutral conductor (grounded circuit conductor) between the transformer and your service, like poor connections, the GEC current will be high.

Look at the voltage between each phase to the grounded circuit conductor (neutral). It should be balanced or approx the same voltage from each leg to neutral (grounded circuit conductor)

Edit made for Charlie B.

[ October 10, 2003, 01:15 PM: Message edited by: dereckbc ]
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: current on a grounding electrode conductor

(I see Dereck has beaten me to the draw. But I'll post my response anyway.)

I hope you won?t mind my being picky here, but you need to restate your question. You have used words in a not-precise-enough manner. Here?s the problem:

The ?grounded? conductor is also called the neutral.

The ?equipment GROUNDING conductor? is also called the ground.

Which do you mean? (I think you mean the later, and so, apparently, did Dereck.) Also, can you give us an idea of why you are asking? It might help us understand your needs, and help us provide you with a useful answer.
 

ryagesh

Member
Re: current on a grounding electrode conductor

Thanks for the help. As for the situation I have driven an 8' ground rod for the 200A 120/240V single phase service and installed a #2 grounding conductor to supplement the coldwater pipe ground. I am seeing anywhere from 2.0A to 5.0A of current on this conductor. Line to neutral voltage for Phases are 123.7V and 122.7V and that varies at different times of the day. I am suspecting that the neutral is giving me the problem but would appreciate any of your info.
Thanks again,
B.Y.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: current on a grounding electrode conductor

Are you measuring the current on the conductor going to the water pipe or ground rod?

If you see the current on the water pipe bond, have a metallic water service, and you share a transformer with your neighbors, you are probable seeing a return on the water pipe which is normal

[ October 10, 2003, 01:29 PM: Message edited by: dereckbc ]
 

bennie

Esteemed Member
Re: current on a grounding electrode conductor

Does this No.#2 run to the rod then to the water pipe? or are you feeding each electrode separately?

Have you made a current measurement with the service turned off?
 

ryagesh

Member
Re: current on a grounding electrode conductor

#2 to the ground rod only the coldwater pipe is a #4 and the current on it is .7A.
 

bennie

Esteemed Member
Re: current on a grounding electrode conductor

Then I assume the electrodes are fed separately, is that correct?

Make a ground current reading, on both ground conductors, with the power off.
 

tonyi

Senior Member
Re: current on a grounding electrode conductor

Originally posted by ryagesh:
#2 to the ground rod only the coldwater pipe is a #4 and the current on it is .7A.
While not the source of this particular problem you're seeing, the water pipe should be the #2 as it is your primary electrode with the rod supplementing. A #4 or #6 to the rod would be OK.

One of the neighbors probably has a loose neutral or a damaged piece of underground wire somewhere if the current is there with the power off to this building.
 

gwz2

Senior Member
Location
Indiana
Re: current on a grounding electrode conductor

Normally, the Ground Rod GEC should not have very much current on it in comparison with a buried metal water pipe that connects to a cast-iron water main.

If the ground rod is touching a large metal buried item, such as an oil tank, water main, natural gas pipe and the buried water pipe is connected to a non-metallic water main, then the ground rod GEC would " see " the larger current.

It is not un-common for a water pipe electrode to " see " 30 to 50 percent of the ungrounded ( netural ) conductor on a transformer that supplies several dwellings. This could easily be 15 to 20 amps if the service is a 3W service (120V) has an un-balanced load.

If the service is 2W , then the water GEC current could be much higher since the grounded conductor should have the same current as the ungrounded comductor.
 

bennie

Esteemed Member
Re: current on a grounding electrode conductor

The ground electrodes are not bonded (shorted) in this situation.

This is multi-point grounding.

[ October 10, 2003, 03:11 PM: Message edited by: bennie ]
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: current on a grounding electrode conductor

Originally posted by ryagesh:
#2 to the ground rod only the coldwater pipe is a #4 and the current on it is .7A.
First thing is you need to run a # 2 AWG GEC from your service grounded conductor to your cold water pipe. Your ground rod can be bonded from the water pipe or service, makes no difference. The point is the ground rod is not the main electrode.

From the voltages you indicated (they are balanced) leads me to believe you may not have a problem, rather one of you neighbors sharing a transformer has a problem. Turn off all the power and measure the current. If you still have current then its your neighbors problem. If it goes away you might have a problem.
 

brian john

Senior Member
Location
Leesburg, VA
Re: current on a grounding electrode conductor

R:

You have some work to do,

While monitoring the GEC current

Turn off the branch circuits one at a time.

Measure each EGC for each circuit.

Measure the neutral/grounded conductor and the phase conductor or conductors as a group look for net current (If this is a house one NM at a time). Your reading should be ZERO if one is anything but zero check that circuit for downstream neutral grounds. A phase conductor can also result in ground current if the short to ground is through a resistor such as a broken heater element.

If you locate a branch circuit with net current see if you can clamp the branch circuit and GEC simultaneously. Hopefully the reading will be zero amps, if not reverse one of the conductors (branch circuit or GEC.)

As an alternative you could TURN OFF ALL POWER main CB and branch circuit CB’s and isolate the branch circuit neutral/grounded conductors, unplug all appliances and check continuity to ground on the neutral/grounded conductors.

It may take some time if your not familiar with troubling shooting net current issues. BUT STICK WITH IT, this is no different than a troubling shooting a branch circuit with a shorted phase conductor. The problem could be in the branch circuit wiring or an appliance, or I could be totally wrong but try the above.

OH YEAH, if this doesn't work or does work please report back. I like to know.
 

hurk27

Senior Member
Re: current on a grounding electrode conductor

First thing is you need to run a # 2 AWG GEC from your service grounded conductor to your cold water pipe.
Why?"
A 200 amp service is only required to have a #4 min. to the water pipe. there is no max requirement! The EGC to the ground rod is not required to be larger than a #6 but again there is no max requirement! In the NEC he can go as large as he want to but as long as it meets the minimum size.
As far as the current on the GEC to the ground rod, this sounds like a lost neutral on the primary side of the POCO's transformer and should be checked by the POCO. the transformer is getting it's return current through your's and probably your neighbors grounding electrodes.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: current on a grounding electrode conductor

Wayne you are correct about the # 4 AWG GEC, my mistake, did not look it up at the time.

I agree it sounds like a loose neutral from the POCO. It started out sounding like it could have been normal current running through the metallic water pipe, but since he indicated the majority was through the rod rather than the water pipe, I concur the loose neutral from POCO.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: current on a grounding electrode conductor

Wayne, one more note: The reason I used cuation before deciding it is a POCO problem was the voltage readings he cited. They are balanced, and that still bothers me. If had said he measured the bulk of the current on the water pipe I would have concluded it is normal.
 
Status
Not open for further replies.
Top